Abstract:Aiming at the low-friction and high-speed precision of bearings, the factors and key points affecting low friction and high-speed precision were analyzed emphatically. Taking the new energy drive motor as an example, the requirements for low friction and high speed were listed.

Key words:Bearing Low friction High-speed precision

Introduction

Bearings are indispensable key basic components in modern industry and are hailed as the "heart" of mechanical equipment. Their load-bearing capacity will directly affect the technical level of the equipment and is an important criterion for measuring a country's scientific and technological and industrial strength. However, as the downstream industries develop and evolve, traditional rolling bearings are becoming increasingly "overwhelmed". The trend of large-scale and high-speed equipment has emerged. More stringent operating conditions and higher reliability requirements pose brand-new challenges to bearing technology.

After more than 40 years of development, China's bearing industry has made considerable progress in both bearing products and manufacturing levels, and has now achieved a considerable scale and development foundation. With the advancement and development of technology, increasingly higher demands have been placed on the performance and requirements of bearings. This article mainly briefly discusses the development trends of bearing technology from two aspects: low friction and high-speed precision.

Low friction

Tribology technology IS the core technology of bearings, ‌ The notable technical feature of the new generation of bearings is the anti-friction design. Youdaoplaceholder0 Rolling bearings, as opposed to sliding bearings, ‌ themselves are "anti-friction bearings". Youdaoplaceholder0 The challenge of the new generation of anti-friction design is to significantly reduce the already very low frictional torque, ‌ the maximum reduction can even reach 80%.

In the application of new energy vehicles, low-friction bearings are required to reduce energy consumption losses. In the demands of aerospace applications, bearings are required to have low-temperature friction resistance and other properties.Bearing friction is not constant; it depends on some kind of friction phenomenon that occurs in the lubricating film between the rolling elements, raceways and cages. The technical indicators that affect the low friction of bearings mainly include the aspect ratio, ‌ bearing clearance, ‌ bearing wall thickness, ‌ and the special design suitable for extreme (limit) working conditions.

‌ 1) wide diameter ratio: ‌ for radial bearings, ‌ width to diameter ratio (‌ B/d) ‌ usually between 0.35 ~ 1.5, ‌ for the thrust bearing, ‌ big path than ‌, ‌ / D1, D2) usually take 2 or less. Youdaoplaceholder0 Choosing a larger value will increase the bearing capacity of the bearing, ‌ but at the same time it will increase the deformation of the shaft and the sensitivity of the misalignment of the two bearing bores.

2) Bearing clearance: ‌ Bearing clearance has a significant effect on the working performance of the bearing. Youdaoplaceholder0 Excessive clearance may cause increased wear and reduced running accuracy, ‌ while too small clearance may cause overheating and excessive temperature rise of the bearing, ‌ requires a sufficiently large fit clearance. Generally ‌ The diameter clearance of non-lubricated bearings is preferably not less than 0.075mm.

 3) Bearing wall thickness: The influence of running performance becomes more obvious with the increase of bearing volume. Youdaoplaceholder0 Where strength is permitted, the wall thickness of ‌ should be as small as possible, ‌ to minimize impact on performance.

4) Extreme (extreme) working condition design: ‌ In extreme working conditions, ‌ such as a low-temperature vacuum environment, ‌ requires specially designed bearings to adapt to extremely low temperatures and high pressures. Youdaoplaceholder0 For example, ‌ The application of solid-lubricated rolling bearings in the aerospace field, ‌ through high-power combined refrigeration and temperature control of the inner and outer rings, ‌ combined radial and axial electromagnetic loading technology, has achieved friction tests and high-resolution measurement of friction factors (coefficients) of rolling bearings under various extreme conditions coexisting, such as extremely low temperature/wide temperature range and ‌ high vacuum.

High-speed precision

The high and low speeds of bearings are not measured by the rotational speed of the bearings themselves, but are classified by their linear velocity. Bearings with a general linear speed of 60 meters per second can be regarded as high-speed bearings. High-speed bearings usually have a smoother surface, and the distance between the inner and outer rings is very small. Therefore, higher requirements are placed on the precision of the bearings. The main factors influencing the high speed of bearings include bearing type, ‌ size, ‌ load, ‌ lubrication method, ‌ material and type of cage, ‌ bearing load, ‌ preload, ‌ drive method, ‌ size of bearing clearance and bearing combination.

1) Bearing type and size: ‌‌ different types of bearings differ in structure and material. The larger the ‌ size, the larger the ‌ moment of inertia, ‌‌ which will affect the speed of the bearing.

2) Load: ‌ The greater the load on the bearing, ‌ the greater the frictional resistance, ‌, which affects the rotational speed.

3) Lubrication method: ‌ Appropriate lubrication method can reduce friction and wear, ‌ increase the rotational speed of the bearing.

4) Cage material and type: ‌ also affects the speed of the bearing. ‌

5) bearing load: ‌ limit rotational speed is under certain load of rolling bearings, ‌ lubrication condition at the highest speed, ‌ and bearing type lubricating way direction, the size of the ‌, ‌, ‌, ‌ clearance, ‌ keep frame structure, ‌ cooling conditions and so on all have very big concern. ‌

6) Preload: ‌ Excessive preload will cause the contact stress between the rolling elements and the raceway surface to increase, ‌ heat generation to rise, ‌ further increase the preload inside the bearing, ‌ make the bearing more prone to wear, ‌ reduce the limiting speed.

7) Drive mode: ‌ Different spindle drive mode will affect the limit speed of the bearing, ‌ such as electric spindle drive, ‌ if the outer cylinder cooling is used at the same time, ‌ may cause the temperature difference between the inner and outer ring of the bearing to become larger, ‌ increase the internal load, ‌ leading to a decrease in the limit speed.

‌8) The size of bearing clearance: The size of the clearance has an important impact on the operating performance and life of the bearing, ‌ appropriate clearance can improve the bearing bearing capacity and limit speed.

‌9) Bearing combination: ‌ By providing a large amount of oil to quickly take away the heat generated by the bearing, ‌ can increase the limit speed.

Conclusion

Take the application of the electric drive system of new energy vehicles as an example. Youdaoplaceholder0 bearings need to meet the characteristics of long service life, ‌ creep resistance, ‌ high speed, ‌ low friction and ‌ low vibration (noise). The starting torque is required to be below 0.002 N.m, and the DmN value of the rotational speed is required to be above 1.8 million mm·r/min. At present, in the field of low-friction bearings, SKF, NSK, JTEKT, Renben and others hold leading market shares globally. In the field of high-speed precision small and medium-sized bearings, SKF, NTN, Bahuan and others have a leading market share globally.